Analysis of the measurement method of traditional lithium battery self-discharge rate

Because the self-discharge rate of lithium batteries is generally low. The self-discharge rate itself is affected by factors such as temperature, cycle times, and SOC. Therefore, it is very difficult and time-consuming to accurately measure the self-discharge of the battery. 1 Traditional self-discharge rate measurement method At present, the traditional self-discharge test method has the following 3 kinds: ● The straight measurement method first charges the tested battery to a certain state of charge, and maintains it for a period of time, and then sets it aside. Discharge to determine the capacity loss of the cell. Self-discharge rate: traditional lithium battery self-discharge rate measurement method where: C is the rated capacity of the battery; C1 is the discharge capacity. After the open circuit is left, the remaining capacity of the battery can be obtained by discharging the battery. At this time, perform multiple charge and discharge cycles on the battery again to determine the full capacity of the electric garlic at this time. This method can determine the irreversible capacity loss and reversible capacity loss of the battery. ●Open circuit voltage decay rate measurement method The open circuit voltage has a direct relationship with the battery state of charge SOC. As long as the change rate of the battery OCV is measured over a period of time, that is: the method is simple to operate, and only needs to record the battery voltage in any time period. Then according to the corresponding relationship between the voltage and the battery SOC, the state of charge of the battery at that moment can be obtained. Through the calculation of the attenuation slope of the voltage and the corresponding attenuation capacity per unit time, the self-discharge rate of the battery can be finally obtained. ●The capacity retention method measures the open-circuit voltage or the amount of power required by the SOC that the battery is expected to maintain to obtain the battery's self-discharge rate. That is to measure the charging current while maintaining the open circuit voltage of the battery, and the battery self-discharge rate can be regarded as the measured charging current. 2 Fast measurement method of self-discharge rate Because the traditional measurement method requires a long time and the measurement accuracy is insufficient, the self-discharge rate is only used as a way to screen whether the battery is qualified in most cases in the battery test process. The emergence of a large number of novel and convenient measurement methods has saved a lot of time and energy for the measurement of battery self-discharge. ●Digital control technology Digital control technology is a new type of self-discharge measurement method derived from the traditional self-discharge measurement method using single-chip microcomputers, etc. This method has the advantages of short measurement time, high accuracy, and simple equipment. ●Equivalent circuit method The equivalent circuit method is a brand-new self-discharge measurement method, which simulates the battery as an equivalent circuit, which can quickly and effectively measure the self-discharge rate of the lithium battery. As an important performance index of lithium batteries, self-discharge rate has an important influence on the selection and configuration of batteries. Therefore, measuring the self-discharge rate of lithium batteries has far-reaching significance. 1 Predicting the problem batteries The same batch of batteries, the materials used and the manufacturing control are basically the same. When the white discharge of individual batteries is clearly too large, the reason is likely to be a serious micro short circuit due to impurities and burrs piercing the diaphragm. Because the impact of micro-short circuit on the battery is slow and irreversible. Therefore, the performance of this type of battery in a short period of time will not differ too much from the normal battery, but after a long-term storage, as the internal irreversible reaction gradually deepens, the performance of the battery will be far lower than its factory performance and other normal battery performance. Therefore, in order to ensure the quality of the factory battery, the battery with large self-discharge has to be eliminated. 2. The battery should be matched with lithium batteries to have better consistency, including capacity, voltage, internal resistance and white discharge rate. The self-discharge rate of the battery has a major impact on the battery pack as follows: once assembled into a module, due to the different self-discharge rate of each single lithium battery, the voltage will drop to varying degrees during the shelving or cycling process, and in series charging The current will be equal again, so after each charge, there may be overcharged or non-overfilled single cells in the lithium battery module. As the number of charging and discharging increases, the battery performance will gradually deteriorate and the cycle life Compared with the unmatched single battery, it is significantly reduced. Therefore, battery packs require accurate measurement and screening of the self-discharge rate of lithium batteries. 3 Battery SOC estimation and corrected state of charge is also called remaining power, which represents the ratio of the remaining capacity of the battery after a period of time or long-term use and its fully charged state. It is often expressed as a percentage. The self-discharge rate has important reference value for the SOC estimation of lithium batteries. The correction of the initial value of SOC by self-discharge current can improve the accuracy of SOC estimation. On the one hand, customers can estimate the usable time or driving distance of the product based on the remaining power; on the other hand, improving the SOC prediction accuracy of BMS can effectively prevent battery overcharging. Over-discharge, thereby extending battery life. Disclaimer: Some pictures and content of articles published on this site are from the Internet. 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